Refractory material and the activation thereof



Patented ar. 27, 1928.

WILLIAM BENJAMIN GERO, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTING- HOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

REFRACTORY MATERIAL AND THE ACTIVATION THEREOF.

No Drawing.

This invention relates to refractory material and methods of activation for electronemission purposes, and more particularly to such material as thoriated tungsten and the activation thereof, prior to working the same to finished sizes of wire.

An object of my invention is the activation of thoria-ted refractory metal, such as tungsten, molybdenum, tantalum and similar metals while inthe form of a bar or slug, by means of gaseous reducing material.

Another object of my invention is the treatment of material such as thoriated tungsten, molybdenum, tantalum and similar thcriated metals before drawing to final form, by heating to a high temperature in a carbon-bearing reducing atmosphere to de velop free thorium therein, to improve the emissivity thereof.

A further object of my invention is the activation of thoriated tungsten and the like, by subjecting it while heated, in a relatively porous condition with respect to gases and before drawing, to the action of hydrocarbon or other carbon-bearing reducing gases or vapors.

A still further object of my invention is to prepare a filamentary body for use as a cathode in electron devices which will not require any special activating process when incorporated as a part of such device.

Other objects and advantages of the inven tion will become apparent upon reading the following description.

Various methods have been devised for producing material for electron-emission purposes. Such methods usually consist in treating a refractory metal Wire or filament after the same has been drawn to final or finished size. Two general types of activation have been employed. One comprises the coating of Wire or filamentary material with oxides, such as the alkaline earths, which have good electron-emitting properties and the other comprises the use of some metal of high atomic weight, such as thorium, as the active electron-emitter. In this application I am concerned with activation by means of thorium or other like metal.

In the copending application of Ralph Serial No. 652,184.

Myers, Serial No. 578,470 filed July 29, 1922, Activation of thoriated filaments and asslgned to the Westinghouse Lamp Company, is disclosed a method of preparing thoriated filamentary material with its surface so modified, that upon heating as a cathode in an electron device, free thorium is developed on the surface thereof, which thereby greatly increases its electron emissivity.

The process disclosed in said' application comprises essentially, the passing of a thoriated filament or wire, white heated, through a hydrocarbon atmosphere whereby the thoria content in the filament is either reduced to thorium, changed to thorium car bide or a mixture comprising one or more of the following materials is formed in or on the filament :thorium, thorium carbide and tungsten carbide. The process disclosed in said application is applicable for adapting material in finished filamentary form only, for activation and introduction into an electron device.

According to my inwention, I prepare refractory metal, suitable for making electronemitting filament or wire, in slug or bar form and so conditioned that the same may be swaged and drawn to the desired wire or filamentary form and used without further treatment as the electron-ernitting filament in an evacuated device. The material preferably used for this purpose is tungsten in powdered form, which has incorporated therewith, a small proportion of powdered 'th-oria, for example, about 1% by weight. 85 This material may then be formed into a slug or bar by pressing. Such slu or bar may be treated while heated to a high temperature in a carbon-bearing reducing atmosphere before or after working and before drawing to a finished size of wire.

The treatment in the carbon-bearing atmosphere may be performed in different ways. For example, the pressed slug may be either treated in a vacuum, hydrogen or similar gas and then subjected to the action of the activating agent, for example, a hydrocarbon gas or Vapor, while at a suitable temperature, or the treating and activating may be combined in one operation, by treat- 109 ing the slug in a vacuum chamber or one containing a reducing or inert atmosphere and admitting the activating gas into the chamber when the ingot or slug has reached the proper temperature.

After activation or treatment as before described, theslug may be swaged and drawn to Wire or filamentary form, according to the usual method of making drawn tungsten wire. Such wire may then be employed as cathode material in electron devices, where it has been found to give good electron-emission, comparable with that obtained from thorium-activated material produced by other methods, with the additional advantage that no treatment for activation purposes, is required after introduction into an electron device, as is often necessary when employing other methods.

The reason for the superiority of wire prepared by this process is not clearly understood. Various theories could-be advanced to explain it, all of which appear inadequate. It has been suggested that since the activation is performed on relatively large sizes that the porosity of the unworked or little worked material renders it readily accessible to the activating gas. It is also possible that the application of heat and work to the material after activation serves to diffuse the activating agent thoroughly throughout the mass and thus assist in the activation by bringing the reacting material into intimate contact, so that the reaction goes to completion more readily.

My invention will better be understood from the following more detailed description of a preferred embodiment thereof.

Tungsten powder, produced according to standard methods, may be prepared with about 1% of thoria incorporated therewith. Such material may be pressed into a bar or slug, about 16 inches long and about 4 inch square, as is usual in the manufacture of tungsten wire. Such a slug is then preferably treated in hydrogen for about 12 minutes while heated by a 'current of about 1700 amperes, which is about 93% of the current required to fuse it, passed therethrough. In other words, the slug is preferably 'sintered inhydrogen at a high temperature, as is usual.

Such a slug or a portion thereof, either before or after 'swaging or otherwise working, may then be treated in a vacuum chamber while subjected to a gradually increasing current passed therethrough. When heated to a temperature approximating about of its fusion temperature, for example, in the neighborhood of about 1800 (l, a hydrocarbon gas or vapor or other carbonaceous or carbon-bearing reducing gas or vapor, for example, benzene or asolme is admitted for about 30 seconds. fter this,

the treating chamber is again evacuated and the heating current turned off.

A specific example of the treatment given 9 inches of a slug, as before mentioned, is as follows:

Schedule. Vacuum condition.

- McLoed Time. Volts. Amperes. gauge Spectrum tube.

10:51 25 0 27 Slight flash. 10:52 25 400 30 10:53 50 500 30 10:54 2. 00 700 97 Steady flash. 10:56 3. 25 800 100+ 10:57 4. 25 1000 100+ 10:58 4. 1200 100+ Whenthe heating current through the slug was finally increased to 1200 amperes, the vacuum pumps were stopped and benzene was admitted for 30 seconds. The pumps were then operated to again evacuate the treating chamber and the current turned off. A slug given the foregoing treatment was swaged and drawn according to usual practice for making tungsten wire and no difiiculty was experienced.

Microphotographs of slugs treated according to my invention show that the carbonizing effect of. the treating gas or vapor extends in from the surface of the treated slug to some degree, after which the interior appears to be unaffected. After such material has been worked or swaged and retreated or annealed, however, the line of demarcation entirely disappears, showing that solution had taken place.

Very good results were obtained by using wire drawn from bars or slugs treated according to my invention, which indicates that good actlvation is obtained by such a process and an emissivity secured equivalent to that obtained from metallic thorium. Among the advantages secured by my invention is greater speed of activation, as it is obvious that a bar or slug about 4 inch square and 16 inches long contains enough material to be drawn into several miles of wire, which if activated by usual methods when in final form would require a long time. Wire manufactured according to the aforedescribed process is in an activated condition and requires no special seasoning or heat-treating schedule to complete the activation thereof, as has been necessary when .flother processes are employed. The slug or bar is merely activated as described and drawn to finished size or sizes afterwards by an suitable known method.

Alt ough I have described What I now consider a preferred embodiment of my invention, it is to be understood that modifications .may occur to those skilled in the art within the spirit and scope of the appended claims.

What is claimed is:

1. The method of activating thoriated refractory metal comprising treating the same before drawing to final size in an atmosphere reducing with respect to thoria.

2. The method of activating thoriated material comprising treating the same in the form of a relatively porous bar or slug in an atmosphere reducing with respect to thoria.

3. The method of activating thoriated refractorg metal comprising pressing the same into a ar or slug and heating in a carbonbearing reducing atmosphere prior to drawing said slug to a finished size of wire.

4. The method of activating thoriated material comprising pressing the same, in powdered form, into a bar or slug and heating said slug in a carbon-bearing reducing atmosphere.v

5. The method of making activated filamentary material comprisin' subjecting thoriated refractory metal, begore the same is drawn to a finished size of wire, to the action of a carbon-bearing reducing atmosphere, while the same is highly heated.

6. The method of activating thoriated refractory metal comprising forming a bar or slug from the same in powdered form and heating said slug to a high de ree in a carbonaceous atmosphere to deve op free thorium therein.

7. The method of activating thoriated tungsten comprising pressing the same in powdered form into a bar or slug and heating said slug to a high degree in a carbonbearing reducing atmosphere to precondition the same for giving thorium-emission, when used as the cathode in an electron device.

8. The method of treating thoriated tungsten for electron-emission purposes comprising forming a pressed bar or slug from the same in powdered form, sintering said slug and heating to ahigh degree in an atmos phere comprising a hydrocarbon fluid.

9. The method of making activated filamentary material comprising subjecting thoriated refractory metal in the form of a relatively porous bar or slug to the action of a carbon-bearing reducing atmosphere while the same is highly-heated.

10. The. method of treating thoriated tungsten to develop thorium emissivity therein comprising heating the same in the form of a bar or slug, relatively porous with respect to gas and vapor, in a carbon-bearing reducing atmosphere.

11. The method of treating thoriated tungsten to develop thorium emissivity therein, comprising heating the same while in the form of a relatively-coarse unfinished bar in a carbon-bearing reducing atmosphere and drawing said bar to wire of the desired size.

12. The method of making activated filamentary material comprising pressing the same while in powdered form into a bar or slug, heating in a carbon-bearing reducing atmosphere and subsequently working the same to wire of the desired size.

13. The method of activating thoriated tungsten for electron-emission purposes comprising pressing the same into a bar or slug, sintering said slug, heating to a high degree in a carbonaceous reducing atmosphere, swaging and drawing said material to wire of the desired size.

In testimony whereof, I have hereunto subscribed my name this 16th day of July,

WILLIAM BENJAMIN GERO. 

